Gas shield for load-break cable terminations

ABSTRACT

A high voltage electric cable termination module characterized by having a gas-confining flange mounted thereon adjacent an end of the module that is used to mount an exposed electrical conductor which is adapted to be engaged and disengaged with a second electrical conductor under loadbreak conditions. The gasconfining shield serves to prevent hot ionized gases generated by an electric arc between the two conductors upon their disengagement or engagement from forming a conductive path between either of the conductors and an electrically conductive coating on the termination module.

United States Patent Kotski Reissued Nov. 4, 1975 54] GAS SHIELD FORLOAD-BREAK CABLE 3,243,756 3/1966 R6616 61 a]... 339/143 R x 3,512,1185/1970 Leonard 339/60 c Reissue of:

TERMINATIONS Edward J. Kotski, Lenox, Mass.

Assignee: General Electric Company Filed: Mar. 5, 1975 Appl. No.2555,385

Related US. Patent Documents Inventor:

3,587,035 7 June 22, 1971 856,671

Sept. 10, 1969 Patent No.: Issued: Appl. No.: Filed:

US. Cl. 339/111; 339/143 R Int. Cl. HOIR 13/52 Field of Search......339/111, 121, 61 R, 143 R,

References Cited UNITED STATES PATENTS 6/1939 Schneider 339/143 RPrimary ExaminerGranville Y. Custer, Jr. Assistant ExaminerDeWalden W.Jones Attorney, Agent, or Firm-Francis X. Doyle [57] ABSTRACT A highvoltage electric cable termination module characterized by having agas-confining flange mounted thereon adjacent an end of the module thatis used to mount an exposed electrical conductor which is adapted to beengaged and disengaged with a second electrical conductor underloadbreak conditions. The gas-confining shield serves to prevent hotionized gases generated by an electric are between the two conductorsupon their disengagement or engagement from forming a conductive pathbetween either of the conductors and an electrically conductive coatingon the termination modulev 7 Claims, 2 Drawing Figures GAS SHIELD FORLOAD-BREAK CABLE TERMINATIONS Matter enclosed in heavy brackets I: '1appears in the original patent but forms no part of this reissuespecification; matter printed in italics indicates the additions made byreissue.

High voltage electrical conductors such as those used in powertransmission and distribution systems tend to develop corona at pointsof mechanical discontinuity or irregularity along their length. Thisproblem is particularly acute at cable junctions where a number ofsurface irregularities and at least one conductor discontinuity areformed. In order to minimize the undesirable resultant radio noise andother objectionable effects of such corona, it is common practice toprovide electrical shielding for such systems to minimize the distortioncreated in the conductors electrical field by such surfaceirregularities. For example, on present day underground electricaldistribution systems, the conducting cable for such systems is usuallywound in an electrically conductive steel shield that serves as a groundplane over the length of the cable. At cable terminations or junctionsin such a system, modular cable terminations, formed of an insulatinghousing having a conductive ground plane mounted thereon, are providedto maintain this shielding function. In use, conductors mounted in suchterminations are electrically connected to the cables and the groundcoatings on the respective terminations are electrically connected tothe cables steel shield, so that when the termination module isconnected to another module the ground planes on the modules form asmooth, continuous conductive circuit around the conductor coupling orjunction formed by the modules.

Until recently, it has been standard practice to open underground cabletermination junctions only when the power distribution system in whichthey are connected has been de-energized. However, load-break deviceshave now been developed for such modules so they may be safely openedunder load conditions. Of course, when a pair of cable terminationmodules are opened or separated under load conditions, an arc isgenerally formed between the conductors of the respective modules. Priorto the present invention, the formation of such an arc created adangerous situation that could cause damage to one of the modules.Specifically, when an arc was formed between prior art cable terminationmodules, hot ionized gases were blasted out of the cable junction intocontact with the conductive ground plane coating on one of theterminations, thus, forming an electrically conductive path between oneor both of the high voltage conductors in the termination modules andground potential at the conductive ground plane coating. This conductivepath was capable of establishing an are that could severely burn thetermination module housing and make it unfit for further use.

An object of the present invention is to provide an electric cabletermination module having improved arc gas confining means that functionto obviate the foregoing problem.

Another object of the invention is to provide a cable termination modulethat is safer to operate and less expensive to produce than prior arttermination modules.

A still further object of the invention is to provide a cabletermination module with an integral gas-confining shield that directsarc-generated gases in a predetermined direction away from theconductive ground plane coating on the module.

Other objects and advantages of the invention will become apparent fromthe following description taken in conjunction with the accompanyingdrawing.

Briefly stated, in one preferred form of the invention an electric cabletermination module having a high voltage electrical conductor mounted ina recess of its insulating housing is provided with a conductive groundplane substantially surrounding the housing and the high voltageconductor, and an insulating gas shield is mounted on the housing at theperipheral edge of the recess. The gas shield projects outwardly fromthe housing between the high voltage conductor mounted in the recess andthe electrically conductive ground coating on the module thereby to forma gas confining means that serves to direct hot ionized gases, generatedwhen the high voltage conductor forms an arc, in a direction away fromthe ground coating on the module.

FIG. 1 of the drawing illustrates a pair of electrical cable terminationmodules shown in spaced-apart relation in a side elevation view, partlyin cross-section, to clearly demonstrate the characteristic features ofthe present invention which is embodied therein.

FIG. 2 of the drawing shows a side elevation view of the modulesdepicted in FIG. 1 connected together in their normal operatingposition.

Referring now to FIG. 1 of the drawing, there is shown a voltage-gradingcable termination module 1 having an insulating housing 2 in which ismounted a rod-like copper electrical conductor 3 that is adapted to beconnected to a high voltage electrical cable 4 (shown in phantom). Inorder to electrically shield the irregularities and discontinuities ofthe electrical conductor and cable junction within module 1,substantially the entire outer surface area of module 1, except theflange portion that will be discussed below, is covered by anelectrically conductive coating 5, which may be formed of a conductiveelastomeric material of any suitable type taken from those well known inthe present art. In like manner, the insulating housing 2 of module 1may be formed of rubber or epoxy or some other suitable insulatingmaterial that is well known in the art. In the preferred form of theinvention, an elastomeric material is used to form housing 2. It will beunderstood that the cable 4 forms part of an electrical powerdistribution system that serves to connect conductor 3 in module 1 to asource of electric power. Thus, when the system is energized, conductor3 is maintained at a high voltage.

Pursuant to the present invention, an integral annular flange is formedaround the outer peripheral edge of a recess 6 in the insulating housing2 around the end of conductor 3. This flange 7 takes the form of a shortcylinder in the preferred form of the invention, as shown in FIG. 1, butit will be understood that other flange configurations may be utilizedto afford the gas confining and channeling functions that will bedescribed in greater detail below. At this point, it is important tofacilitate an understanding of the invention to note that the outersurface of flange 7 is not covered by the conductive ground coating 5.Therefore, it will be seen that the flange 7 increases the electricalflash-over distance between conductor 3 and the ground coating 5, andalso that the insulating flange 7 is positioned in a gas- 3 shieldingposition between these respective conductive members to afford theshielding function that will be discussed below.

In order to fully describe the functions and advantages of my invention,there is also shown in FIG. 1 a second cable termination module 8 thatcomprises an insulating housing 9 having a conductive ground coating 10over a major portion of its outer surface. Module 8 houses a secondconductor 11 that is provided with a plurality of resilient fingers 12which are adapted to engage conductor 3 in module 1 when the modules 1and 8 are moved together and connected in operating position. It will beunderstood that the conductive ground plane coating 10 on module 8terminates at ridge 13 thereon, so that when modules 1 and 8 areconnected in operating position the conductive coating on ridge 13 is inclose proximity to the terminal end of conductive coating 5 on module 1,with only the insulating flange 7 therebetween. Thus, the respectiveground plane coatings form a substantially uniform electric fieldthrough the insulating material of flange 7 at this junction, withrespect to the energized conductors 3 and 11 in modules 1 and 8.

It should be understood that the electric circuit from cable 4 throughconductors 3 and 11 is completed back to the above-mentioneddistribution system by conductor 11 being electrically connected to asecond high voltage insulated electric cable 14, which may be connectedto a distribution transformer or other system component (not shown). Ifthe cable 14 is connected to a vault-mounted transformer that generatesa substantialamount of heat, it may be found to be desirable to use ahigh temperature resistant cable for cable 14, in the manner discussedmore fully in co-pending U.S. Pat. application Ser. No. 688,832, whichwas filed Dec. 7, 1967 and is assigned to the assignee of the presentinvention. In order to appreciate the advantages of the presentinvention, it should be understood that a cylindrically shaped rod 15 ofarc quenching material is mounted on the end of conductor 3 and acooperating cylinder 16 of arc quenchinng material is glued to the wallsof an insulating cylinder 17 that serves to mount the cylinder 16 in apredetermined position with respect to the housing 9 and conductor 11.In the preferred embodiment of the invention, the arc-quenchingmaterials 15 and 16 can be formed of a gas evloving acrylic material ora suitable resin such as Celcon, which is a tradename for a resinmaterial manufactured and sold by the Celanese Corporatin of America.

In the operation of the present invention, when termination module 1 ismoved into operating position with respect to termination module 8, asshown in FIG.

2 of the drawing, the inner surface of recess 6 forms a water-tight,voltage grading connection with the outer conically shaped surface 18 ofmodule 8, and conductor 3 is in electrical engagement with the fingers12 of conductor 11. When it is desired to open or disengage thiscircuit, a hotstick or other suitable handling means is engaged in theholding loop 19 on module 1 and through this means force is applied tothe module 1 to pull it away from module 8. As conductor 3 separatesfrom the fingers 12 of conductor 11, an arc is formed between these twoconductive members and this are is squeezed between the arcextinguishing rod 15 and cylinder 16. This confinement of the arc inclose proximity to these arc-extinguishing cylinders generates asubstantial volume of hot ionized gases which are blown up into recess 6and then outwardly in the direction shown by the arrows in FIG. 1. Dueto the configuration of flange 7 which is provided on module 1 pursuantto the present invention, and due to its operating position on the edgeof conically shaped recess 6, these hot ionized gases are forced to movein a direction away from the conductive coating 5 on module 1.Therefore, the gases are prevented from forming a low resistanceconductive path between either conductor 3 or conductor 11 and theground coating 5.

It will be noted that the hot ionized gases are forced to move towardthe ground coating 10 on module 8; however, this direction of movementdoes not introduce an appreciable risk of damage to module 8 because bythe time the gases have moved into contact with the coating 10, theyhave been sufficiently dispersed and cooled by the direction of movementthat they have been forced through by flange 7 so that they aredeionized and do not form a low resistance conductive path betweenconductor 3 and the coating 10 on module 8. Accordingly, it can be seenthat with the protective gasshielding flange 7 of the present invention,the risk of flashover to ground following a gas-generating, load-breakdisconnect operation of the modules 1 and 8 is obviated. It will beapparent to those skilled in the art that other shapes of thegas-shielding flange 7 may be utilized in other embodiments of theinvention; however, in the preferred embodiment of the invention thegenerally cylindrically formed walls of flange 7 i which substantiallyparallel the longitudinal axis of conductor 3 and project outwardly fromthe end of conductor 3 have been found to be particularly suitable forunderground distribution systems where the conductor termination modules1 and 8 are often subjected to appreciable amounts of moisture. Inparticular, it will be noted that the flange 7 is formed of a resilientelastomeric insulating material in the preferred form of the inventionand this flange 7 is adapted to cooperate with a raised rib 20 on themodule 8 as shown clearly in FIG. 2 of the drawing, to further enhancethe waterproof seal formed between modules 1 and 8 when they are intheir respective operating positions.

What I claim and desire to secure by Letters Patent of the United Statesis:

1. A voltage-grading termination module comprising an insulating housinghaving an electrical conductor mounted therein to form an electricalcircuit through the housing from a first point adjacent one end thereofto a second point adjacent another end thereof, means defining a recessin said housing around the electrical conductor at said one end thereof,an annular flange of insulating material disposed entirely around theoutermost peripheral edge of said recess and projecting outwardly andaway from the end of said conductor in the recess thereby to form a gasconfining shield around said end of the conductor, and a coating ofelectrically conductive material mounted on the outer surface of saidhousing to cover substantially the entire area thereof up to but notincluding the outer surface of said flange, said recess being generallyfrustoconical in shape with its large diameter end abutting theinnermost end of said flange thereby to form a gas confining chamber andshield arrangement that operates to direct arc-generated gas in adirection away from said coating, said end of said conductor beingoperable to engage and disengage a second electrical conductor and toform a gas-generating are between itself and said second conductorduring such engaging and disengaging operations, said gas confiningshield being effective to prevent such arc-generated gas from forming aconductive path between either of said conductors and said coating saidannular flange comprising an integral part ofsaid insulating housing.

[2. A termination module as defined in claim 1 wherein said annularflange comprises an integral part of said insulating housing] 3. Atermination module as defined in claim 1 wherein said flange iscylindrical in form and has its central longitudinal axis disposed insubstantial alignment with a longitudinal axis of the conductor in saidrecess.

4. A termination module as defined in claim 1 wherein said insulatinghousing is formed of resilient material.

5. A termination module as defined in claim 4 wherein said coatingcomprises an elastomeric material.

6. A termination module as defined in claim 3 wherein substantially theentire cylinder wall area of said flange is disposed outward from theoutermost end of the conductor in said recess.

7. a termination module as defined in claim 5 wherein said coating doesnot occupy more than of the surface area of said housing, but does format least one continuous electrically conductive circuit between the twoends of said housing.

8. A termination module as defined in claim 5 wherein said flange ofinsulating material is formed of a material having a dielectric constantthat enables a uniform electric field to be formed through it from theterminal end of said conductive coating to the terminal end of a secondconductive coating disposed adjacent the inner surface of said flangeapproximately under the terminal end of said coating.

1. A voltage-grading termination module comprising an insulating housinghaving an electrical conductor mounted therein to form an electricalcircuit through the housing from a first point adjacent one end thereofto a second point adjacent another end thereof, means defining a recessin said housing around the electrical conductor at said one end thereof,an annular flange of insulating material disposed entirely around theoutermost peripheral edge of said recess and projecting outwardly andaway from the end of said conductor in the recess thereby to form a gasconfining shield around said end of the conductor, and a coating ofelectrically conductive material mounted on the outer surface of saidhousing to cover substantially the entire area thereof up to but notincluding the outer surface of said flange, said recess being generallyfrusto-conical in shape with its large diameter end abutting theinnermost end of said flange thereby to form a gas confining chamber andshield arrangement that operates to direct arc-generated gas in adirection away from said coating, said end of said conductor beingoperable to engage and disengage a second electrical conductor and toform a gas-generating arc between itself and said second conductorduring such engaging and disengaging operations, said gas confiningshield being effective to prevent such arc-generated gas from forming aconductive path between either of said conductors and said coating (.) ,said annular flange comprising an integral part of said insulatinghousing.
 3. A termination module as defined in claim 1 wherein saidflange is cylindrical in form and has its central longitudinal axisdisposed in substantial alignment with a longitudinal axis of theconductor in said recess.
 4. A termination module as defined in claim 1wherein said insulating housing is formed of resilient material.
 5. Atermination module as defined in claim 4 wherein said coating comprisesan elastomeric material.
 6. A termination module as defined in claim 3wherein substantially the entire cylinder wall area of said flange isdisposed outward from the outermost end of the conductor in said recess.7. a termination module as defined in Claim 5 wherein said coating doesnot occupy more than 90% of the surface area of said housing, but doesform at least one continuous electrically conductive circuit between thetwo ends of said housing.
 8. A termination module as defined in claim 5wherein said flange of insulating material is formed of a materialhaving a dielectric constant that enables a uniform electric field to beformed through it from the terminal end of said conductive coating tothe terminal end of a second conductive coating disposed adjacent theinner surface of said flange approximately under the terminal end ofsaid coating.